Liquid phase chromatography and extraction techniques are dependent on the interaction of a region bonded to a solid support and a solvent environment containing the solutes of interest. The support is stationary with respect to the liquid or solvent phase. The interacting region is designated as a “bonded-phase” or “interphase.” An overview of this technology is provided by C. Horvath in Silylated Surfaces ed. D. Leyden, Gordon & Breach 1980 p. 269, the contents of which are incorporated herein by reference. Features which make a bonded phase desirable are reproducible non-bonding interactions with solutes in the mobile phase under a variety of operating conditions including temperature, pressure, and nature of solvent and the stability over a period of time.
The most widely used bonded phases are hydrophobic phases derived from octadecyl functional silanes. Specifically, octadecyldimethylchlorosilane and octadecyltrichlorosilane treated silicas are most widely used in high pressure liquid chromatography and solid-phase extraction, respectively.
Hydrophobic phases frequently must be “conditioned” with an organic solvent prior to applying analytical samples in dissolved aqueous or mixed solvent water mixtures or utilizing aqueous or mixed solvent water mixtures as mobile phases in order to achieve acceptable results. One approach to eliminating the need for conditioning is to apply a silane which contains a polar group in relatively close proximity to the point of attachment of the silane to the inorganic substrate. This approach is sometimes referred to as buried or embedded hydrophilicity. In general, these phases suffer from column bleed, i.e., the slow loss of the bonded phase observed either directly in changes in elution base-line or indirectly by loss in efficacy of separation. The introduction of polar groups close to the attachment of the silane to the substrate, while solving the problem of conditioning, brings water molecules to the substrate surface where they can effect a hydrolysis of Si—O—Si bonds. The problem is particularly exacerbated in the most common phases with embedded hydrophilicity that contain polar protic groups such as amides or urethanes. Similar issues occur in DNA and protein array technology in which substitutents on the bonded phase are more complex structures associated with peptides or oligonucleotides. The technologies often utilize immobilization technology and carry out analysis at greater pH ranges particularly at pH>7.0 where the scission of Si—O—Si is accelerated. Dipodal silanes with buried amines are discussed by McGall and Forman, U.S. Pat. No. 6,743,882, however these materials do not possess optimum stability because the diamine structure can be particularly active in dissolution of silicon dioxide surfaces.
Thus, there is a need in the art to provide bonded phases with embedded hydrophilicity which provide stable bonds with the a substrate and which allow for interaction of solutes with the hydrophobic bonded portion in a water and/or solvent environment with minimal negative effects in the form of bed collapse, diffusion or detachment of the bonded phase.